A unique method for measuring filtration in single isolated glomeruli has been developed. This technique permits study of the ultrafiltration characteristics in glomeruli from any animal and from superficial and deep cortical regions. Glomeruli may be studied under a variety of conditions. We have established a standard condition for study of glomerular function in vitro and have investigated filtration in normal dogs, rats, and rabbits. We have begun to study changes which occur with maturation and during several types of renal injury. Results will lead to a better understanding of the process of glomerular filtration and the factors which alter glomerular function in health and disease.